2 use std::collections::BTreeMap;
4 use rustc_errors::DiagnosticBuilder;
6 use rustc_hir::intravisit::{walk_body, walk_expr, walk_inf, walk_ty, Visitor};
7 use rustc_hir::{Body, Expr, ExprKind, GenericArg, Item, ItemKind, QPath, TyKind};
8 use rustc_lint::{LateContext, LateLintPass, LintContext};
9 use rustc_middle::hir::nested_filter;
10 use rustc_middle::lint::in_external_macro;
11 use rustc_middle::ty::{Ty, TyS, TypeckResults};
12 use rustc_session::{declare_lint_pass, declare_tool_lint};
13 use rustc_span::source_map::Span;
14 use rustc_span::symbol::sym;
15 use rustc_typeck::hir_ty_to_ty;
17 use if_chain::if_chain;
19 use clippy_utils::diagnostics::{multispan_sugg, span_lint_and_then};
20 use clippy_utils::differing_macro_contexts;
21 use clippy_utils::source::{snippet, snippet_opt};
22 use clippy_utils::ty::is_type_diagnostic_item;
24 declare_clippy_lint! {
26 /// Checks for public `impl` or `fn` missing generalization
27 /// over different hashers and implicitly defaulting to the default hashing
28 /// algorithm (`SipHash`).
30 /// ### Why is this bad?
31 /// `HashMap` or `HashSet` with custom hashers cannot be
34 /// ### Known problems
35 /// Suggestions for replacing constructors can contain
36 /// false-positives. Also applying suggestions can require modification of other
37 /// pieces of code, possibly including external crates.
41 /// # use std::collections::HashMap;
42 /// # use std::hash::{Hash, BuildHasher};
43 /// # trait Serialize {};
44 /// impl<K: Hash + Eq, V> Serialize for HashMap<K, V> { }
46 /// pub fn foo(map: &mut HashMap<i32, i32>) { }
48 /// could be rewritten as
50 /// # use std::collections::HashMap;
51 /// # use std::hash::{Hash, BuildHasher};
52 /// # trait Serialize {};
53 /// impl<K: Hash + Eq, V, S: BuildHasher> Serialize for HashMap<K, V, S> { }
55 /// pub fn foo<S: BuildHasher>(map: &mut HashMap<i32, i32, S>) { }
57 #[clippy::version = "pre 1.29.0"]
60 "missing generalization over different hashers"
63 declare_lint_pass!(ImplicitHasher => [IMPLICIT_HASHER]);
65 impl<'tcx> LateLintPass<'tcx> for ImplicitHasher {
66 #[allow(clippy::cast_possible_truncation, clippy::too_many_lines)]
67 fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
68 use rustc_span::BytePos;
71 cx: &LateContext<'tcx>,
72 diag: &mut DiagnosticBuilder<'_>,
74 generics_suggestion_span: Span,
75 target: &ImplicitHasherType<'_>,
76 vis: ImplicitHasherConstructorVisitor<'_, '_, '_>,
78 let generics_snip = snippet(cx, generics_span, "");
80 let generics_snip = if generics_snip.is_empty() {
83 &generics_snip[1..generics_snip.len() - 1]
88 "consider adding a type parameter",
91 generics_suggestion_span,
93 "<{}{}S: ::std::hash::BuildHasher{}>",
95 if generics_snip.is_empty() { "" } else { ", " },
96 if vis.suggestions.is_empty() {
99 // request users to add `Default` bound so that generic constructors can be used
106 format!("{}<{}, S>", target.type_name(), target.type_arguments(),),
111 if !vis.suggestions.is_empty() {
112 multispan_sugg(diag, "...and use generic constructor", vis.suggestions);
116 if !cx.access_levels.is_exported(item.def_id) {
121 ItemKind::Impl(ref impl_) => {
122 let mut vis = ImplicitHasherTypeVisitor::new(cx);
123 vis.visit_ty(impl_.self_ty);
125 for target in &vis.found {
126 if differing_macro_contexts(item.span, target.span()) {
130 let generics_suggestion_span = impl_.generics.span.substitute_dummy({
131 let pos = snippet_opt(cx, item.span.until(target.span()))
132 .and_then(|snip| Some(item.span.lo() + BytePos(snip.find("impl")? as u32 + 4)));
133 if let Some(pos) = pos {
134 Span::new(pos, pos, item.span.ctxt(), item.span.parent())
140 let mut ctr_vis = ImplicitHasherConstructorVisitor::new(cx, target);
141 for item in impl_.items.iter().map(|item| cx.tcx.hir().impl_item(item.id)) {
142 ctr_vis.visit_impl_item(item);
150 "impl for `{}` should be generalized over different hashers",
154 suggestion(cx, diag, impl_.generics.span, generics_suggestion_span, target, ctr_vis);
159 ItemKind::Fn(ref sig, ref generics, body_id) => {
160 let body = cx.tcx.hir().body(body_id);
162 for ty in sig.decl.inputs {
163 let mut vis = ImplicitHasherTypeVisitor::new(cx);
166 for target in &vis.found {
167 if in_external_macro(cx.sess(), generics.span) {
170 let generics_suggestion_span = generics.span.substitute_dummy({
171 let pos = snippet_opt(
175 body.params[0].pat.span.lo(),
181 let i = snip.find("fn")?;
182 Some(item.span.lo() + BytePos((i + (&snip[i..]).find('(')?) as u32))
184 .expect("failed to create span for type parameters");
185 Span::new(pos, pos, item.span.ctxt(), item.span.parent())
188 let mut ctr_vis = ImplicitHasherConstructorVisitor::new(cx, target);
189 ctr_vis.visit_body(body);
196 "parameter of type `{}` should be generalized over different hashers",
200 suggestion(cx, diag, generics.span, generics_suggestion_span, target, ctr_vis);
211 enum ImplicitHasherType<'tcx> {
212 HashMap(Span, Ty<'tcx>, Cow<'static, str>, Cow<'static, str>),
213 HashSet(Span, Ty<'tcx>, Cow<'static, str>),
216 impl<'tcx> ImplicitHasherType<'tcx> {
217 /// Checks that `ty` is a target type without a `BuildHasher`.
218 fn new(cx: &LateContext<'tcx>, hir_ty: &hir::Ty<'_>) -> Option<Self> {
219 if let TyKind::Path(QPath::Resolved(None, path)) = hir_ty.kind {
220 let params: Vec<_> = path
228 .filter_map(|arg| match arg {
229 GenericArg::Type(ty) => Some(ty),
233 let params_len = params.len();
235 let ty = hir_ty_to_ty(cx.tcx, hir_ty);
237 if is_type_diagnostic_item(cx, ty, sym::HashMap) && params_len == 2 {
238 Some(ImplicitHasherType::HashMap(
241 snippet(cx, params[0].span, "K"),
242 snippet(cx, params[1].span, "V"),
244 } else if is_type_diagnostic_item(cx, ty, sym::HashSet) && params_len == 1 {
245 Some(ImplicitHasherType::HashSet(
248 snippet(cx, params[0].span, "T"),
258 fn type_name(&self) -> &'static str {
260 ImplicitHasherType::HashMap(..) => "HashMap",
261 ImplicitHasherType::HashSet(..) => "HashSet",
265 fn type_arguments(&self) -> String {
267 ImplicitHasherType::HashMap(.., ref k, ref v) => format!("{}, {}", k, v),
268 ImplicitHasherType::HashSet(.., ref t) => format!("{}", t),
272 fn ty(&self) -> Ty<'tcx> {
274 ImplicitHasherType::HashMap(_, ty, ..) | ImplicitHasherType::HashSet(_, ty, ..) => ty,
278 fn span(&self) -> Span {
280 ImplicitHasherType::HashMap(span, ..) | ImplicitHasherType::HashSet(span, ..) => span,
285 struct ImplicitHasherTypeVisitor<'a, 'tcx> {
286 cx: &'a LateContext<'tcx>,
287 found: Vec<ImplicitHasherType<'tcx>>,
290 impl<'a, 'tcx> ImplicitHasherTypeVisitor<'a, 'tcx> {
291 fn new(cx: &'a LateContext<'tcx>) -> Self {
292 Self { cx, found: vec![] }
296 impl<'a, 'tcx> Visitor<'tcx> for ImplicitHasherTypeVisitor<'a, 'tcx> {
297 fn visit_ty(&mut self, t: &'tcx hir::Ty<'_>) {
298 if let Some(target) = ImplicitHasherType::new(self.cx, t) {
299 self.found.push(target);
305 fn visit_infer(&mut self, inf: &'tcx hir::InferArg) {
306 if let Some(target) = ImplicitHasherType::new(self.cx, &inf.to_ty()) {
307 self.found.push(target);
314 /// Looks for default-hasher-dependent constructors like `HashMap::new`.
315 struct ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
316 cx: &'a LateContext<'tcx>,
317 maybe_typeck_results: Option<&'tcx TypeckResults<'tcx>>,
318 target: &'b ImplicitHasherType<'tcx>,
319 suggestions: BTreeMap<Span, String>,
322 impl<'a, 'b, 'tcx> ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
323 fn new(cx: &'a LateContext<'tcx>, target: &'b ImplicitHasherType<'tcx>) -> Self {
326 maybe_typeck_results: cx.maybe_typeck_results(),
328 suggestions: BTreeMap::new(),
333 impl<'a, 'b, 'tcx> Visitor<'tcx> for ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
334 type NestedFilter = nested_filter::OnlyBodies;
336 fn visit_body(&mut self, body: &'tcx Body<'_>) {
337 let old_maybe_typeck_results = self.maybe_typeck_results.replace(self.cx.tcx.typeck_body(body.id()));
338 walk_body(self, body);
339 self.maybe_typeck_results = old_maybe_typeck_results;
342 fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
344 if let ExprKind::Call(fun, args) = e.kind;
345 if let ExprKind::Path(QPath::TypeRelative(ty, method)) = fun.kind;
346 if let TyKind::Path(QPath::Resolved(None, ty_path)) = ty.kind;
347 if let Some(ty_did) = ty_path.res.opt_def_id();
349 if !TyS::same_type(self.target.ty(), self.maybe_typeck_results.unwrap().expr_ty(e)) {
353 if self.cx.tcx.is_diagnostic_item(sym::HashMap, ty_did) {
354 if method.ident.name == sym::new {
356 .insert(e.span, "HashMap::default()".to_string());
357 } else if method.ident.name == sym!(with_capacity) {
358 self.suggestions.insert(
361 "HashMap::with_capacity_and_hasher({}, Default::default())",
362 snippet(self.cx, args[0].span, "capacity"),
366 } else if self.cx.tcx.is_diagnostic_item(sym::HashSet, ty_did) {
367 if method.ident.name == sym::new {
369 .insert(e.span, "HashSet::default()".to_string());
370 } else if method.ident.name == sym!(with_capacity) {
371 self.suggestions.insert(
374 "HashSet::with_capacity_and_hasher({}, Default::default())",
375 snippet(self.cx, args[0].span, "capacity"),
386 fn nested_visit_map(&mut self) -> Self::Map {